In the beginning, there was an infinitely dense, tiny ball of matter.
Then, it all went bang, giving rise to the atoms, molecules, stars, and
galaxies we see today. Or at least, that's what we've been told by physicists
for the past several decades.
But new theoretical physics research has recently revealed a possible
window into the very early universe,
showing that it may not be "very early" after all. Instead, it may be
just the latest iteration of a bang-bounce cycle that has been going on for …
well, at least once, and possibly forever. Of course, before physicists
decide to toss out the Big Bang in
favor of a bang-bounce cycle, these theoretical predictions will need to
survive an onslaught of observation tests.
Scientists have a really good picture of the very early universe,
something we know and love as the Big Bang theory. In this model, a long time
ago the universe was far smaller, far hotter, and far denser than it is today.
In that early inferno 13.8 billion years ago, all the elements that make us
what we are were formed in the span of about a dozen minutes.
Even earlier, this thinking goes, at some point, our entire universe — all
the stars, all the galaxies, all the everything — was the size of a peach and had
a temperature of over a quadrillion degrees.
Amazingly, this fantastical story holds up to all current observations.
Astronomers have done everything from observing the leftover electromagnetic
radiation from the young universe to measuring the abundance of the
lightest elements and found that they all line up with what the Big Bang
predicts. As far as we can tell, this is an accurate portrait of our early
universe.
But as good as it is, we know that the Big Bang picture is not complete —
there's a puzzle piece missing, and that piece is the earliest moments of the
universe itself. That's a pretty big piece.
WHAT IS EKPYROTIC THEORY?
The problem is that the physics that we use to understand the early
universe (a wonderfully complicated mishmash of general
relativity and high-energy particle physics) can take us only so far
before breaking down. As we try to push deeper and deeper into the first
moments of our cosmos, the math gets harder and harder to solve, all the way to
the point where it just … quits.
The main sign that we have terrain yet to be explored is the presence of
a "singularity,"
or a point of infinite density, at the beginning of the Big Bang. Taken at face
value, this tells us that at one point, the universe was crammed into an infinitely
tiny, infinitely dense point. This is obviously absurd, and what it really
tells us is that we need new physics to solve this problem — our current
toolkit just isn't good enough.
To save the day, we need some new physics — something that is capable of
handling gravity and the other forces, combined, at ultrahigh energies. And
that's exactly what string theory claims
to be: a model of physics that is capable of handling gravity and the other
forces, combined, at ultrahigh energies. This means that string theory claims
it can explain the earliest moments of the universe.
One of the earliest string theory notions is the "ekpyrotic"
universe, which comes from the Greek word for "conflagration," or
fire. In this scenario, what we know as the Big Bang was sparked by something
else happening before it — the Big Bang was not a beginning, but one part of a
larger process.
Extending the ekpyrotic concept has led to a theory, again motivated by
string theory, called cyclic cosmology. I suppose that, technically, the idea
of the universe continually repeating itself is thousands of years old and
predates physics, but string theory gave the idea firm mathematical grounding.
The cyclic universe goes about exactly as you might imagine, continually
bouncing between big bangs and big crunches, potentially for eternity back in
time and for eternity into the future.
WHAT HAPPENED BEFORE THE BIG BANG?
As cool as this sounds, early versions of the cyclic model had difficulty
matching observations — which is a major deal when you're trying to do science
and not just telling stories around the campfire.
The main hurdle was agreeing with our observations of the cosmic
microwave background, the fossil light leftover from when the universe was
only 380,000 years old. While we can't see directly past that wall of light, if
you start theoretically tinkering with the physics of the infant cosmos, you
affect that afterglow light pattern.
And so, it seemed that a cyclic universe was a neat but incorrect idea.
But the ekpyrotic torch has been kept lit over the years, and a paper published in March 2020 has explored the
wrinkles in mathematics and uncovered some previously missed opportunities.
The two physicists who authored the study, Robert Brandenberger and Ziwei Wang,
both of McGill University in Canada, found that in the moment of the
"bounce," when our universe shrinks to an incredibly small point and
returns to a Big Bang state, it's possible to line everything up to get the proper
observationally tested result.
In other words, the complicated (and, admittedly, poorly understood)
physics of this critical epoch may indeed allow for a radically revised view of
our time and place in the cosmos.
But to fully test this model, we'll have to wait for a new generation of cosmology experiments. So let's wait to break out the ekpyrotic champagne.